KVM: x86: Check non-canonical addresses upon WRMSR

Upon WRMSR, the CPU should inject #GP if a non-canonical value (address) is
written to certain MSRs. The behavior is "almost" identical for AMD and Intel
(ignoring MSRs that are not implemented in either architecture since they would
anyhow #GP). However, IA32_SYSENTER_ESP and IA32_SYSENTER_EIP cause #GP if
non-canonical address is written on Intel but not on AMD (which ignores the top
32-bits).

Accordingly, this patch injects a #GP on the MSRs which behave identically on
Intel and AMD.  To eliminate the differences between the architecutres, the
value which is written to IA32_SYSENTER_ESP and IA32_SYSENTER_EIP is turned to
canonical value before writing instead of injecting a #GP.

Some references from Intel and AMD manuals:

According to Intel SDM description of WRMSR instruction #GP is expected on
WRMSR "If the source register contains a non-canonical address and ECX
specifies one of the following MSRs: IA32_DS_AREA, IA32_FS_BASE, IA32_GS_BASE,
IA32_KERNEL_GS_BASE, IA32_LSTAR, IA32_SYSENTER_EIP, IA32_SYSENTER_ESP."

According to AMD manual instruction manual:
LSTAR/CSTAR (SYSCALL): "The WRMSR instruction loads the target RIP into the
LSTAR and CSTAR registers.  If an RIP written by WRMSR is not in canonical
form, a general-protection exception (#GP) occurs."
IA32_GS_BASE and IA32_FS_BASE (WRFSBASE/WRGSBASE): "The address written to the
base field must be in canonical form or a #GP fault will occur."
IA32_KERNEL_GS_BASE (SWAPGS): "The address stored in the KernelGSbase MSR must
be in canonical form."

This patch fixes CVE-2014-3610.

Cc: stable@vger.kernel.org
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7d603a71ab3a9f36ea6729e2924b998e3a83c556..ccc94de4ac499db2681af23ae2b457ec5e813ff5 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -989,6 +989,20 @@ static inline void kvm_inject_gp(struct kvm_vcpu *vcpu, u32 error_code)
        kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
 }
 
+static inline u64 get_canonical(u64 la)
+{
+       return ((int64_t)la << 16) >> 16;
+}
+
+static inline bool is_noncanonical_address(u64 la)
+{
+#ifdef CONFIG_X86_64
+       return get_canonical(la) != la;
+#else
+       return false;
+#endif
+}
+
 #define TSS_IOPB_BASE_OFFSET 0x66
 #define TSS_BASE_SIZE 0x68
 #define TSS_IOPB_SIZE (65536 / 8)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 65510f624dfe2a42571bc22e73d8755a23e801e5..00bed2c5e948a1bdc7a58fbe345b0ce057ce4d64 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3251,7 +3251,7 @@ static int wrmsr_interception(struct vcpu_svm *svm)
        msr.host_initiated = false;
 
        svm->next_rip = kvm_rip_read(&svm->vcpu) + 2;
-       if (svm_set_msr(&svm->vcpu, &msr)) {
+       if (kvm_set_msr(&svm->vcpu, &msr)) {
                trace_kvm_msr_write_ex(ecx, data);
                kvm_inject_gp(&svm->vcpu, 0);
        } else {

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 0acac81f198b0b03c83b4f4f9ef86178fa84f821..148020a7dd980e061d31649cd46f70fa4e7e7228 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5291,7 +5291,7 @@ static int handle_wrmsr(struct kvm_vcpu *vcpu)
        msr.data = data;
        msr.index = ecx;
        msr.host_initiated = false;
-       if (vmx_set_msr(vcpu, &msr) != 0) {
+       if (kvm_set_msr(vcpu, &msr) != 0) {
                trace_kvm_msr_write_ex(ecx, data);
                kvm_inject_gp(vcpu, 0);
                return 1;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 34c8f94331f83dad10ff80f6b3f1fafa861b9ed6..5a7195573a327b263aee6ded80c07a34714e784b 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -987,7 +987,6 @@ void kvm_enable_efer_bits(u64 mask)
 }
 EXPORT_SYMBOL_GPL(kvm_enable_efer_bits);
 
-
 /*
  * Writes msr value into into the appropriate "register".
  * Returns 0 on success, non-0 otherwise.
@@ -995,8 +994,34 @@ EXPORT_SYMBOL_GPL(kvm_enable_efer_bits);
  */
 int kvm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
+       switch (msr->index) {
+       case MSR_FS_BASE:
+       case MSR_GS_BASE:
+       case MSR_KERNEL_GS_BASE:
+       case MSR_CSTAR:
+       case MSR_LSTAR:
+               if (is_noncanonical_address(msr->data))
+                       return 1;
+               break;
+       case MSR_IA32_SYSENTER_EIP:
+       case MSR_IA32_SYSENTER_ESP:
+               /*
+                * IA32_SYSENTER_ESP and IA32_SYSENTER_EIP cause #GP if
+                * non-canonical address is written on Intel but not on
+                * AMD (which ignores the top 32-bits, because it does
+                * not implement 64-bit SYSENTER).
+                *
+                * 64-bit code should hence be able to write a non-canonical
+                * value on AMD.  Making the address canonical ensures that
+                * vmentry does not fail on Intel after writing a non-canonical
+                * value, and that something deterministic happens if the guest
+                * invokes 64-bit SYSENTER.
+                */
+               msr->data = get_canonical(msr->data);
+       }
        return kvm_x86_ops->set_msr(vcpu, msr);
 }
+EXPORT_SYMBOL_GPL(kvm_set_msr);
 
 /*
  * Adapt set_msr() to msr_io()'s calling convention